Remove the old mechanism of generating a CMake toolchain file on the fly when 'emconfigure cmake' is called. Instead, the Emscripten toolchain file in Emscripten\cmake\Platform\Emscripten.cmake is always used. This unifies the CMake toolchain handling to use the same toolchain independent of how CMake gets invoked.
Have test_cmake also test that running 'emconfigure cmake' works, in addition to running cmake directly.